WO2022188136A1

WO2022188136A1 - Electrochemical device and electronic apparatus

Info

Publication number: WO2022188136A1
Application number: PCT/CN2021/080416
Authority: WO
Inventors: 李娅洁
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-03-12
Filing date: 2021-03-12
Publication date: 2022-09-15
Also published as: CN113853699B; EP4300615A1; US20230420687A1; CN113853699A

Abstract

An electrochemical device and an electronic apparatus. The electrochemical device comprises a positive electrode; the positive electrode comprises a positive electrode active material layer; the positive electrode active material layer comprises a positive electrode active material and a composite carbon material; the volume of the positive electrode active material layer is a first volume A; the volume of pores having a pore diameter of less than 2 μm in the positive electrode active material layer is a second volume B, wherein 14%≤B/A≤20%. The positive electrode active material layer comprises the positive electrode active material and the composite carbon material, and 14%≤B/A≤20%, 14%≤B/A≤20% indicating that the formed positive electrode has abundant pores for lithium ion transport.

Description

Electrochemical and electronic devices

technical field

The present application relates to the field of electrochemical energy storage, in particular to electrochemical devices and electronic devices.

Background technique

With the development and advancement of electrochemical devices (eg, lithium-ion batteries), higher and higher requirements have been placed on their rate performance and energy density. Although the current technologies for improving electrochemical devices can improve the rate performance and energy density of electrochemical devices to a certain extent, they are still unsatisfactory, and further improvements are expected.

SUMMARY OF THE INVENTION

Some embodiments of the present application provide an electrochemical device that includes a positive electrode, the positive electrode includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material and a composite carbon material. The volume of the positive electrode active material layer is the first volume A, and the volume of pores with a diameter of less than 2 μm in the positive electrode active material layer is the second volume B, where 14%≤B/A≤20%.

In some embodiments, the volume of pores with a pore diameter of less than or equal to 200 nm in the positive electrode active material layer is the third volume C, 24%≤C/B≤36%. In some embodiments, the composite carbon material includes carbon nanotubes and two-dimensional inorganic materials. In some embodiments, the tube length of the carbon nanotubes is greater than or equal to 2 μm. In some embodiments, the two-dimensional inorganic material includes at least one of graphene, V ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ , Co ₃ V ₂ O ₈ , MoS ₂ or SnO ₂ . In some embodiments, the mass ratio of carbon nanotubes and the two-dimensional inorganic material is greater than or equal to 1 and less than or equal to 20. In some embodiments, the Dv50 of the two-dimensional inorganic material is less than 8 μm.

In some embodiments, the mass content of the positive electrode active material in the positive electrode active material layer is greater than or equal to 97%. In some embodiments, the compaction density of the positive electrode active material layer is less than or equal to 4.2 g/cm ³ . In some embodiments, the resistance of the positive active material layer is less than 0.2Ω. In some embodiments, the electrochemical device adopts a 4C discharge rate test with a capacity retention rate of ≥80%.

In some embodiments, the electrochemical device further includes a negative electrode that includes a negative electrode active material layer. In some embodiments, the mass content of the negative electrode active material in the negative electrode active material layer is greater than or equal to 97.4%. In some embodiments, the compaction density of the negative active material layer is less than or equal to 1.7 g/cm ³ . In some embodiments, the negative active material includes at least one of graphite, hard carbon, silicon, silicon oxide, or organosilicon.

Embodiments of the present application also provide an electronic device, including the above electrochemical device.

In the embodiments of the present application, by making the positive electrode active material layer include a positive electrode active material and a composite carbon material, the composite carbon material can play the role of structural bonding and pore formation. On the one hand, since the composite carbon material is used to replace the existing polymer adhesive The binding agent makes the lithium ion production process more environmentally friendly and is conducive to improving the energy density of lithium ion batteries. On the other hand, the use of composite carbon materials makes the volume B of the pores with a diameter of less than 2 μm in the positive active material layer and the volume of the positive active material layer. The ratio of A is: 14%≤B/A≤20%, which indicates that the formed cathode has abundant pores for lithium ion transport, which is beneficial to improve the rate performance of lithium ion batteries.

Detailed ways

The following examples may enable those skilled in the art to more fully understand the present application, but do not limit the present application in any way.

Some embodiments of the present application provide an electrochemical device including a positive electrode including a positive electrode active material layer. In some embodiments, the positive electrode active material layer includes a positive electrode active material and a composite carbon material. In some embodiments, the volume of the positive electrode active material layer is the first volume A, and the volume of pores with a pore diameter of less than 2 μm in the positive electrode active material layer is the second volume B, where 14%≤B/A≤20%. The above pore volumes can be tested by the pore volume test method discussed below, but this is only exemplary and other suitable methods can be used. In some embodiments, the porosity of the positive electrode active material layer may be adjusted by cold pressing pressure, but this is only exemplary and not intended to limit the present application.

The composite carbon material in the positive electrode active material layer can play the role of structural bonding and pore formation. 14%≤B/A indicates that the formed positive electrode has abundant pores for lithium ion transport, thereby improving the electrical conductivity formed by the positive electrode. Rate capability of chemical devices. If the B/A is too small, for example, less than 14%, the positive electrode active layer is unfavorable for lithium ion transport, reducing the rate capability of the electrochemical device. However, if the B/A is too large, eg, 20%<B/A, the energy density of the electrochemical device is adversely affected.

In some embodiments, the volume of pores with a pore diameter of less than or equal to 200 nm in the positive electrode active material layer is the third volume C, 24%≤C/B≤36%. The more pores with pore size ≤200nm, the more abundant the lithium ion transport channels, which is more conducive to the rapid deintercalation of lithium ions on the surface of the active material, which is particularly important for fast charging capability. The cathode with 24%≤C/B has better rate performance. , and enables the electrochemical device to achieve a capacity retention rate of more than 80% at a 4C discharge rate. If C/B is too small, the rapid deintercalation of lithium ions on the surface of the active material cannot be sufficiently achieved. In addition, if the C/B is too large, for example, 36% < C/B, it indicates that there are too many small particles inside, the small particles are easy to agglomerate, and poor dispersion may adversely affect the resistance of the active material layer, which in turn affects the rate performance of the electrochemical device. .

In some embodiments, the composite carbon material includes carbon nanotubes (CNTs) and two-dimensional inorganic materials. CNTs overlap each other on the surface of the positive electrode active material, which plays the role of structural bonding. Two-dimensional inorganic materials can exist at the overlap between the positive electrode active material and CNTs, forming strong bonding and good conductive sites, which also play a role in creating The role of small pores (eg, pores with a pore size ≤ 200 nm). In some embodiments, carbon nanotubes can be single-walled, multi-walled, or few-walled. The two-dimensional inorganic material in the present application refers to an inorganic material in which electrons can move freely (planar motion) only on the nanoscale (1 nm to 100 nm) in two dimensions.

In some embodiments, the tube length of the carbon nanotubes is greater than or equal to 2 μm. Carbon nanotubes with larger tube lengths can play a better role in structural bonding. In some embodiments, the two-dimensional inorganic material includes at least one of graphene, V ₂ O ₅ , Nb ₂ O ₅ , TiO ₂ , Co ₃ V ₂ O ₈ , MoS ₂ or SnO ₂ . In some embodiments, the mass ratio of the carbon nanotubes and the two-dimensional inorganic material is greater than or equal to 1 and less than or equal to 20. If the mass ratio of carbon nanotubes and two-dimensional inorganic materials is too small, the content of carbon nanotubes is relatively small, and the structural bonding of carbon nanotubes will be affected to a certain extent. If the ratio is too large, the effect of enhancing adhesion, increasing conductive sites and creating small pores of the two-dimensional inorganic material may be adversely affected. In some embodiments, the Dv50 of the two-dimensional inorganic material is less than 8 μm. If the Dv50 of the two-dimensional inorganic material is too large, the conductive properties of the cathode active material layer will be adversely affected.

In some embodiments, the positive active material includes lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadyl phosphate, sodium vanadyl phosphate, lithium vanadate, manganese At least one of lithium oxide, lithium nickelate, lithium nickel cobalt manganese oxide, lithium rich manganese based material or lithium nickel cobalt aluminate. In some embodiments, the positive electrode active material layer may further include a conductive agent. In some embodiments, the conductive agent in the positive active material layer may include at least one of conductive carbon black, Ketjen black, lamellar graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the mass content of the positive electrode active material in the positive electrode active material layer is greater than or equal to 97%. By using a higher mass content of the positive active material, the energy density of the corresponding electrochemical device can be improved. In some embodiments, the compaction density of the positive electrode active material layer is less than or equal to 4.2 g/cm ³ . If the compaction density of the positive electrode active material layer is too large, the internal resistance of lithium ion transport may be increased, which is not conducive to the rapid transport of lithium ions. In some embodiments, the resistance of the positive active material layer may be less than 0.2Ω. Therefore, it is beneficial to improve the kinetic performance of the corresponding electrochemical device.

In some embodiments, the composite carbon material functions as a binder in the positive electrode active material layer. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent and the composite carbon material in the positive electrode active material layer may be (95-99.5):(0-1):(0.5-5). In some embodiments, the thickness of the cathode active material layer may be 10 μm to 500 μm. It should be understood that the above description is only an example, and the positive electrode active material layer of the positive electrode may adopt any other suitable material, thickness and mass ratio.

In some embodiments, the positive electrode may further include a positive electrode current collector on which the positive electrode active material layer is disposed. In some embodiments, the cathode active material layer is disposed on one or both sides of the cathode current collector. In some embodiments, the positive electrode current collector may use Al foil, and of course, other positive electrode current collectors commonly used in the art may also be used. In some embodiments, the thickness of the cathode current collector may be 1 μm to 200 μm. In some embodiments, the cathode active material layer may be coated only on a partial area of the cathode current collector.

In some embodiments, the electrochemical device may also include a negative electrode. In some embodiments, the electrochemical device may include an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

In some embodiments, the negative electrode includes a negative electrode active material layer. In some embodiments, the anode active material layer includes an anode active material, and the anode active material may include at least one of graphite, hard carbon, silicon, silicon oxide, or organic silicon. In some embodiments, the mass content of the negative electrode active material in the negative electrode active material layer is greater than or equal to 97.4%. By using a higher mass content of the negative electrode active material, the energy density of the electrochemical device formed from the negative electrode can be increased. In some embodiments, the compaction density of the negative electrode active material layer is less than or equal to 1.7 g/cm ³ under the condition that the stored electricity is discharged. If the compaction density of the negative electrode active material layer is too large, the internal resistance of lithium ion transport may be increased, which is not conducive to the rapid transport of lithium ions, and lithium is easily precipitated during the charging process of the electrochemical device.

In some embodiments, a conductive agent and a binder may also be included in the anode active material layer. In some embodiments, the conductive agent in the negative active material layer may include at least one of conductive carbon black, Ketjen black, lamellar graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the binder in the negative active material layer may include carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysilicon At least one of oxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin or polyfluorene. In some embodiments, the mass ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode active material layer may be (90˜98):(0.1˜10):(0.1˜10). It should be understood that the above are only examples and any other suitable materials and mass ratios may be employed.

In some embodiments, the negative electrode may further include a negative electrode current collector, and the negative electrode active material layer is disposed on one or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may use at least one of copper foil, nickel foil or carbon-based current collector.

In some embodiments, the release membrane includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene or ultra-high molecular weight polyethylene. Especially polyethylene and polypropylene, they have a good effect on preventing short circuits and can improve the stability of the battery through the shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 5 μm to 50 μm.

In some embodiments, the surface of the separator may further include a porous layer, the porous layer is disposed on at least one surface of the substrate of the separator, the porous layer includes inorganic particles and a binder, and the inorganic particles are selected from alumina (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), titanium oxide (TiO ₂ ), hafnium dioxide (HfO ₂ ), tin oxide (SnO ₂ ), ceria (CeO ₂ ), nickel oxide (NiO) ), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO ₂ ), yttrium oxide (Y ₂ O ₃ ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, hydroxide At least one of calcium or barium sulfate. In some embodiments, the pores of the isolation membrane have diameters in the range of about 0.01 μm to 1 μm. The binder of the porous layer is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyamide At least one of vinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The porous layer on the surface of the separator can improve the heat resistance, oxidation resistance and electrolyte wettability of the separator, and enhance the adhesion between the separator and the pole piece.

In some embodiments of the present application, the electrode assembly of the electrochemical device is a wound electrode assembly, a stacked electrode assembly, or a folded electrode assembly. In some embodiments, the positive electrode and/or the negative electrode of the electrochemical device may be a multi-layer structure formed by winding or stacking, or may be a single-layer structure in which a single-layer positive electrode, a separator, and a single-layer negative electrode are stacked.

In some embodiments, the electrochemical device includes a lithium-ion battery, although the present application is not so limited. In some embodiments, the electrochemical device may also include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution, and the electrolytic solution includes a lithium salt and a non-aqueous solvent. _The lithium salt is selected from LiPF6, _LiBF4 , LiAsF6, _LiClO4 , LiB ₍ _C6H5 ₎ ₄ , _LiCH3SO3 , _LiCF3SO3 , LiN ₍ _SO2CF3 ₎ ₂ , _LiC ₍ _SO2CF3 ) ₃ , LiSiF ₆ , LiBOB or one or more of lithium difluoroborate. For example, LiPF ₆ is chosen as the lithium salt because it has high ionic conductivity and can improve cycle characteristics.

The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.

The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.

Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl carbonate Ethyl esters (MEC) and combinations thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), or a combination thereof. Examples of the fluorocarbonate compound are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate Fluoroethylene, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-carbonate -Difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.

Examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decolactone, Valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

Examples of ether compounds are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxy Ethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, methyl amide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.

In some embodiments of the present application, taking a lithium-ion battery as an example, the positive electrode, the separator, and the negative electrode are wound or stacked in sequence to form electrode parts, and then packed into, for example, an aluminum-plastic film for encapsulation, injected with electrolyte, and formed into, Encapsulation, that is, to make a lithium-ion battery. Then, the performance test of the prepared lithium-ion battery was carried out.

Those skilled in the art will understand that the methods of making electrochemical devices (eg, lithium ion batteries) described above are only examples. Other methods commonly used in the art may be employed without departing from the disclosure of the present application.

Embodiments of the present application also provide electronic devices including the above electrochemical devices. The electronic device in the embodiment of the present application is not particularly limited, and it may be used in any electronic device known in the prior art. In some embodiments, electronic devices may include, but are not limited to, notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, assisted bicycles, bicycles, Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large-scale household storage batteries and lithium-ion capacitors, etc.

Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein a lithium-ion battery is used as an example.

Example 1

Preparation of the positive electrode: The positive active material lithium cobalt oxide, conductive carbon black, carbon nanotubes, and two-dimensional inorganic material titanium dioxide (TiO ₂ ) were dissolved in N-methylpyrrolidone (NMP) in a weight ratio of 98.2:0.5:1.182:0.118 ) solution to form a positive electrode slurry. Using aluminum foil as the positive electrode current collector, the positive electrode slurry is coated on the positive electrode current collector to obtain a positive electrode active material layer, and the positive electrode is obtained after drying, cold pressing and cutting.

Preparation of negative electrode: Graphite, sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene rubber were dissolved in deionized water in a weight ratio of 97.8:1.3:0.9 to form a negative electrode slurry. Using a copper foil with a thickness of 10 μm as the negative electrode current collector, the negative electrode slurry was coated on the negative electrode current collector, dried, and cut to obtain a negative electrode.

Preparation of isolation film: The isolation film substrate is polyethylene (PE) with a thickness of 8 μm, and 2 μm alumina ceramic layers are coated on both sides of the isolation film substrate, and finally, 2.5 μm alumina ceramic layers are coated on both sides of the coated ceramic layer. mg/cm ² binder polyvinylidene fluoride (PVDF), dried.

Preparation of electrolyte: LiPF ₆ was added to a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC), acrylate: subcarbonate in an environment with a water content of less than 10 ppm Vinyl ester (VC)=20:30:20:28:2, weight ratio), the concentration of LiPF ₆ is 1.15 mol/L, and the mixture is uniform to obtain the electrolyte.

Preparation of lithium ion battery: stack the positive electrode, the separator and the negative electrode in sequence, so that the separator is placed between the positive electrode and the negative electrode for isolation, and then the electrode assembly is obtained by winding. The electrode assembly is placed in the outer packaging aluminum-plastic film, and after dehydration at 80°C, the above electrolyte is injected and packaged, and the lithium ion battery is obtained through the process of forming, degassing, and trimming.

In the examples and comparative examples, the parameters are changed on the basis of the steps in Example 1, and the specific parameters to be changed are shown in the following table.

In Examples 2 to 7, the ratio B/A of the volume of pores having a pore diameter of less than 2 μm in the positive electrode active material layer to the volume of the positive electrode active material layer was different from that of Example 1.

In Examples 8 to 14, the ratio C/B of the volume of pores with a pore diameter of 200 nm or less in the positive electrode active material layer and the volume of pores with a pore diameter of less than 2 μm in the positive electrode active material layer was different from Example 4.

In Examples 15 to 21, the kind of the two-dimensional inorganic material was different from that of Example 4.

In Examples 22 to 24, the kinds of carbon nanotubes were different from those in Example 4.

In Examples 25 to 28, the lengths of the carbon nanotubes were different from those of Example 4.

In Examples 29 to 35, the mass ratios of carbon nanotubes and two-dimensional inorganic materials were different from those in Example 4.

In Examples 36 to 39, the Dv50 of the two-dimensional inorganic material was different from that of Example 4.

In Examples 40 to 44, the mass content of the conductive agent in the positive electrode active material layer was different from that in Example 4.

In Examples 45 to 49, the mass content of the positive electrode active material in the positive electrode active material layer was different from that of Example 4.

In Examples 50 to 54, the compaction density of the positive electrode active material layer when the electric charge was discharged was different from that of Example 4.

In Examples 55 to 59, the mass content of the negative electrode active material in the negative electrode active material layer was different from that of Example 4.

In Examples 60 to 64, the compaction density of the negative electrode active material layer when the electric charge was discharged was different from that of Example 4.

In Comparative Examples 1 and 2, polyvinylidene fluoride (PVDF) was used as the binder. In Comparative Examples 3 to 5, the ratio B/A of the volume of pores with a pore diameter of less than 2 μm in the positive electrode active material layer to the volume of the positive electrode active material layer is less than or equal to 14%, and the positive electrode active material layer in Comparative Example 5 has a pore diameter of less than or equal to 200 nm. The ratio of the volume of pores to the volume of pores having a pore diameter of less than 2 μm in the positive electrode active material layer is C/B<24%.

The test methods for each parameter of the present application are described below.

Pore Volume Test:

Autopore V 9620 mercury porosimeter, the test method is as follows:

The cutting mold takes the sample to be tested with a fixed area S, (if the sample to be tested is a sample that has been in contact with the electrolyte, it needs to be soaked and cleaned with DMC solvent for 3 times, soaked for 1 min at a time, and dried until the weight no longer changes before mercury injection test), measure the thickness D1 of the foil with a micrometer, and calculate the volume of the foil in the sample V1=S×D1; put the sample to be tested into the dilatometer sample cell. First, put the dilatometer into the low pressure chamber of the mercury porosimeter, select "low pressure mode" to measure the total volume V of the sample (calculated by deducting the volume of the low pressure mercury input from the standard sample pool of the dilatometer), and the volume of the active material layer A=V-V1; The meter is loaded into the high pressure chamber, and the instrument selects the "high pressure mode" to measure the mercury injection curve, which is the pore distribution curve, and the integral area is the pore volume. The cumulative mercury injection volume corresponding to the pressure with a pore size of ≤2μm is the volume B, and the cumulative mercury injection volume corresponding to the pressure with a pore size ≤200nm is the small pore volume C.

Active material layer resistance test:

The battery was discharged to a 0% state of charge, disassembled to obtain the electrode piece to be measured, and the Japanese BT3562 resistance meter was used for data acquisition. Place the pole piece to be tested on the test sample stage, adjust the air pressure until the measured value of the pressure sensor is in the setting range, and check whether the test pressure head causes damage to the structure of the active material layer. Test after confirming that the air pressure is normal. Using the AC four-terminal test method, load the AC current Is to the active material layer, the sensor collects the voltage drop V _IS caused by the test object, and obtains the corresponding resistance R= _VIS / _IS according to Ohm _'s law.

Compaction Density Test of Active Material Layer:

Discharge the battery to a 0% state of charge, disassemble to obtain the pole piece to be measured, take a pole piece with a known area s from the fixed mold, weigh it and measure the thickness with a micrometer. Deduct the foil weight (known area and density) and thickness (measured with a micrometer). The weight m and thickness h of the active material layer are obtained, and the ratio between the weight and thickness of the active material layer is the compaction density of the active material layer in the discharge state=m/hs.

Capacity retention rate test at 4C discharge rate:

The lithium-ion battery was placed in a constant temperature box at 25°C ± 2°C for 2 hours, charged to 4.48V at a rate of 1C, and then charged to 0.05C at a constant voltage of 4.48V. Discharge at 1C rate to 3.0V for cycle performance test to obtain reference discharge capacity; discharge at 4C rate to 3.0V for cycle performance test to obtain actual discharge capacity, capacity retention rate at 4C discharge rate = actual discharge capacity/reference discharge capacity* 100%.

Table 1 shows the respective parameters and evaluation results of Examples 1 to 7 and Comparative Examples 1, 2 and 4.

Table 1

By comparing Examples 1 to 7 with Comparative Example 1, it can be seen that by using a composite carbon material, and 14%≤B/A≤20%, the resistance of the positive electrode active material layer is significantly reduced, and the electrochemical device has a high discharge rate at 4C. The capacity retention rate is significantly improved.

By comparing Examples 1 to 7 and Comparative Example 3, it can be seen that when 14%≤B/A, the resistance of the positive electrode active material layer does not change much with respect to the case where B/A is equal to 13%, but the electrochemical device discharges at 4C The capacity retention rate under the magnification rate is significantly improved.

By comparing Examples 1 to 7 and Comparative Example 4, it can be seen that when B/A≤20%, the resistance of the positive electrode active material layer does not change much with respect to the case where B/A is equal to 21%, but the electrochemical device discharges at 4C The capacity retention rate under the magnification rate is significantly improved.

Table 2 shows the respective parameters and evaluation results of Examples 8 to 14.

Table 2

By comparing Examples 8 to 14 with Comparative Example 2, it can be seen that when 24%≤C/B≤36%, the resistance of the positive electrode active material layer using the composite carbon material is significantly reduced, and the electrochemical device has a high discharge rate at 4C. The capacity retention rate is significantly improved.

By comparing Examples 8 to 14 and Comparative Example 5, it can be seen that when 24%≤C/B, the resistance of the positive electrode active material layer is reduced relative to the case where C/B is equal to 23%, and the electrochemical device is discharged at a discharge rate of 4C. The capacity retention rate was significantly improved.

By comparing Examples 8 to 14 with Comparative Example 6, it can be seen that when C/B ≤ 36%, the resistance of the positive electrode active material layer is reduced relative to the case where C/B is equal to 37%, and the electrochemical device is discharged at a discharge rate of 4C. The capacity retention rate was significantly improved.

Table 3 shows the respective parameters and evaluation results of Examples 15 to 21 and Comparative Example 3.

table 3

By comparing Examples 15 to 21, it can be seen that with various two-dimensional inorganic materials, the resistance of the positive electrode active material layer does not change much, and the capacity retention rate of the electrochemical device at a discharge rate of 4C does not change much.

By comparing Examples 15 to 21 with Comparative Example 7, when no 2D inorganic material was added, the resistance of the positive electrode active material layer did not change much, but the capacity retention rate of the electrochemical device at a discharge rate of 4C decreased.

Table 4 shows the respective parameters and evaluation results of Examples 22 to 28 and Comparative Example 5.

Table 4

By comparing Examples 22 to 24, it can be seen that with the use of few-walled or single-walled carbon nanotubes, the resistance of the positive active material layer is reduced relative to the use of multi-walled carbon nanotubes, and the capacity of the electrochemical device at a discharge rate of 4C is reduced. Retention rate improved.

By comparing Examples 25 to 28, it can be seen that with the increase of the tube length of the carbon nanotubes, the resistance of the positive electrode active material layer tends to decrease, but the capacity retention rate of the electrochemical device at a discharge rate of 4C decreases to a certain extent. .

By comparing Examples 25 to 28 with Comparative Example 8, it can be seen that when the tube length of the carbon nanotubes is ≥2 μm, the resistance of the positive active material layer does not change much, but the capacity retention rate of the electrochemical device at a discharge rate of 4C is significantly improved.

Table 5 shows the respective parameters and evaluation results of Examples 29 to 35.

table 5

By comparing Examples 29 to 35, it can be seen that as the mass ratio of carbon nanotubes and two-dimensional inorganic material titanium dioxide increases, the resistance of the positive electrode active material layer decreases, but the capacity retention rate of the electrochemical device at a discharge rate of 4C is a certain decline.

Table 6 shows the respective parameters and evaluation results of Examples 36 to 44.

Table 6

By comparing Examples 36 to 39, it can be seen that when the Dv50 of the two-dimensional inorganic material is less than 8 μm, with the increase of the Dv50 of the two-dimensional inorganic material, the resistance of the positive electrode active material layer first decreases and then increases, and the electrochemical device is in the The capacity retention at the 4C discharge rate first increased and then decreased.

By comparing Examples 36 to 39 with Comparative Example 9, it can be seen that when 1 μm<Dv50 of the two-dimensional inorganic material, the resistance of the active material layer is significantly reduced relative to Dv50=0.1 μm, and the capacity of the electrochemical device is maintained at a discharge rate of 4C. rate increased significantly.

By comparing Examples 40 to 44, it can be seen that with the increase of the mass content of the conductive carbon black as the conductive agent, the resistance of the positive electrode active material layer first decreased and then increased, and the capacity retention rate of the electrochemical device at a discharge rate of 4C improved. .

Table 7 shows the respective parameters and evaluation results of Examples 45 to 55.

Table 7

By comparing Examples 45 to 50, it can be seen that as the mass content of the positive electrode active material in the positive electrode active material layer decreases and the mass content of the composite carbon material increases, the resistance of the positive electrode active material layer tends to decrease, and the electrochemical device The capacity retention rate at 4C discharge rate has an upward trend.

By comparing Examples 51 to 55, it can be seen that as the compaction density of the positive electrode active material layer increases, the resistance of the positive electrode active material layer tends to increase, and the capacity retention rate of the electrochemical device at a discharge rate of 4C decreases. trend.

Table 8 shows the respective parameters and evaluation results of Examples 56 to 65.

Table 8

By comparing Examples 56 to 60, it can be seen that with the increase of the mass content of the negative electrode active material in the negative electrode active material layer, the resistance of the positive electrode active material layer does not change much, and the capacity retention of the electrochemical device at a discharge rate of 4C takes the lead. Descend after ascending.

By comparing Examples 61 to 65, it can be seen that with the increase of the compaction density of the negative active material layer, the resistance of the positive active material layer does not change much, and the capacity retention rate of the electrochemical device at a discharge rate of 4C tends to decrease.

The above description is only a preferred embodiment of the present application and an illustration of the applied technical principles. Those skilled in the art should understand that the scope of disclosure involved in this application is not limited to the technical solutions formed by the specific combination of the above-mentioned technical features, but also covers other technical solutions formed by any combination of the above-mentioned technical features or their equivalents. Technical solutions. For example, a technical solution is formed by replacing the above features with the technical features disclosed in the present application with similar functions.

Claims

An electrochemical device, comprising a positive electrode, the positive electrode comprising:

A positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material and a composite carbon material, the volume of the positive electrode active material layer is the first volume A, and the volume of the pores with a pore diameter of less than 2 μm in the positive electrode active material layer is the first volume A. Two volumes B, wherein 14%≤B/A≤20%.
The electrochemical device according to claim 1, wherein the volume of pores with a pore diameter of 200 nm or less in the positive electrode active material layer is a third volume C, wherein 24%≤C/B≤36%.
The electrochemical device of claim 1, wherein the composite carbon material comprises carbon nanotubes and two-dimensional inorganic materials.
The electrochemical device according to claim 3, wherein the tube length of the carbon nanotubes is 2 μm or more.
The electrochemical device of claim 3, wherein the two-dimensional inorganic material comprises graphene, V 2 O 5 , Nb 2 O 5 , TiO 2 , Co 3 V 2 O 8 , MoS 2 or SnO 2 at least one.
The electrochemical device according to claim 3, wherein a mass ratio of the carbon nanotubes and the two-dimensional inorganic material is 1 or more and 20 or less.
The electrochemical device of claim 3, wherein the Dv50 of the two-dimensional inorganic material is less than 8 μm.
The electrochemical device of claim 1, wherein the positive electrode satisfies one of the following conditions:

The mass content of the positive electrode active material in the positive electrode active material layer is greater than or equal to 97%;

The compaction density of the positive electrode active material layer is less than or equal to 4.2 g/cm 3 ;

The resistance of the positive electrode active material layer is less than 0.2Ω.
The electrochemical device according to claim 1, wherein the electrochemical device adopts a 4C discharge rate test, and the capacity retention rate is greater than or equal to 80%.
The electrochemical device according to claim 1, wherein the electrochemical device further comprises a negative electrode, the negative electrode comprises a negative electrode active material layer, and the negative electrode satisfies one of the following conditions:

The mass content of the negative electrode active material in the negative electrode active material layer is greater than or equal to 97.4%;

The compaction density of the negative electrode active material layer is less than or equal to 1.7 g/cm 3 ;

The negative electrode active material includes at least one of graphite, hard carbon, silicon, silicon oxide or organic silicon.
An electronic device comprising the electrochemical device according to any one of claims 1 to 10.